atomic pile vs nuclear reactor

atomic pile and nuclear reactor both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic pile	Yes	No	No	No
nuclear reactor	Yes	No	No	No

As nouns, nuclear reactor is a hypernym of atomic pile; that is, nuclear reactor is a word with a broader meaning than atomic pile:

atomic pile: a nuclear reactor that uses controlled nuclear fission to generate energy
nuclear reactor: (physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements

Other hypernyms of atomic pile include reactor.

atomic pile (noun)	nuclear reactor (noun)
a nuclear reactor that uses controlled nuclear fission to generate energy	(physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements